Many of electrical components equipped in automobiles are composed of combinations of metal conductors and resin insulators. Within these electrical components, a large current on the order of 1 to 100 A flows to metal conductors. In order to prevent the metal conductors, to which a large current flows, from malfunctioning due to moisture, it is required to surely carry out waterproofing treatment on the metal conductors by the resin insulators.
In particular, when moisture infiltrates into the inner parts of the electrical components, some parts built in the electrical components may go out of order, and therefore, electrical components are required to be surely provided with waterproofing mechanisms.
An electrical component is usually manufactured by an insert molding method in order to enhance adhesion between a metal conductor and a resin insulator. However, in an insert molded article formed of the resin insulator and the metal conductor, a metal having a small linear expansion coefficient contacts a resin or a resin composition having a large mold shrinkage factor or a large linear expansion coefficient, and therefore, a large thermal stress is generated between the metal conductor and the resin insulator during injection molding and cooling. Such a large thermal stress may easily cause the occurrence of peeling off at an interface between the metal conductor and the resin insulator, which may cause a problem of deterioration of adhesion at the interface between the metal conductor and the resin insulator. In particular, since the resin insulator contracts significantly during a cooling process after molding, the deterioration of adhesion may easily occur at the interface between the metal conductor and the resin insulator. As a result, a gap may be generated between the metal conductor and the resin insulator, and water may infiltrate from the gap.
Accordingly, it has been considered that the waterproof construction of the electrical component should have a structure through which no moisture can pass even when some moisture enters into the gap between the resin insulator and the metal conductor. For example, by making the structure of the resin insulator have a sufficiently large thickness, it is possible to prevent moisture from infiltrating into the inner parts of the electrical component even if a gap is generated at the interface between the resin insulator and the metal conductor, because the length of the resin insulator from the outside surface to the inside surface at the interface can be lengthened. With regard to parts which particularly require high waterproofing properties, sufficient waterproofing properties can be realized by using a sealing member such as a packing and an O-ring.
By the way, in recent years, in response to a request for miniaturization and weight reduction of an electrical component for the purpose of improving the fuel consumption and the like of an automobile, insert molding which enables the miniaturization has been conducted. As a resin insulator for the miniaturization and weight reduction, engineering plastics which exhibit excellent electrical properties and good heat resistance have been used. As engineering plastics, for example, a polyphenylene sulfide resin, a polybutylene terephthalate resin, a nylon-based resin, a modified polyphenylene ether-based resin and the like have been used.
In particular, in recent years, the polyphenylene sulfide resin, which exhibits a low water absorption property, good dimensional stability and high fluidity, and therefore can realize thin-wall molding, has been increasingly used in electrical components of automobiles.
However, in thin-wall insert molding in which the polyphenylene sulfide resin is used, moisture may infiltrate into the inner parts of the electrical component from a very small gap at the interface between the resin insulator and the metal conductor because the thickness of the resin insulator is small. When water infiltrates from the very small gap at the interface, there are concerns about bad influences on the electronic control, and therefore, an issue of adhesion between the resin and the metal has attracted attention.